Unit 1 Proteins and enzymes Flashcards
How are polypeptides arranged to form the secondary and then the tertiary structure of a protein?
Secondary - hydrogen bonds form between amino acids in chain, automatically coils into alpha helix of beta pleated sheets.
Tertiary - coiled and folded further, more bonds. For proteins made from 1 polypeptide chain this is their final 3D structure.
How are amino acids linked to form polypeptides?
Amino acids are linked together by condensation reactions - molecule of water is released.
Peptide bonds are formed between the amino acids.
How is the quaternary structure of a protein formed?
For proteins that are made from more that one polypeptide chain (e.g. Haemoglobin) the quaternary structure is their final 3D structure. They are made from several polypeptide chains held together by bonds.
How are proteins identified?
The biuret test :
Add sodium hydroxide
Then add copper(II) sulfate solution
If protein is present the solution will turn purple. (If not stay blue)
How do enzymes speed up chemical reactions?
Enzymes lower the activation energy that’s needed so reactions can happen at a lower temperature, speeding up the rate of reaction.
(Enzyme-substrate complex formed which lowers activation energy by:
Allows two molecules to bond together more easily as closer
A strain is out on bonds in substrate so they break up easier )
How does the structure of enzymes relate to their function?
Enzymes have very specific tertiary structure.
Only one substrate will fit with one active site (active site determined by enzymes tertiary structure)
If substrate shape doesn’t match the active site the reaction won’t be catalysed
What is the lock and key model of enzyme action?
The substrate fits into the enzymes active site (same way key fits into lock), the active site and substrate have a complementary shape.
What is the induced fit model of enzyme action?
Substrate is a similar shape to active site and make the active shape change shape in the right way.
Enzyme-substrate complex changes shape slightly to completely fit.
How is the rate of an enzyme-controlled reaction measured?
- Measuring the amount of product produced
2. Measuring amount of substrate left
How does temperature affect the rate of an enzyme-controlled reaction?
Rate of reaction increases when temperature increases
More heat = more kinetic energy so molecules move faster
The substrate molecules are now more likely to collide with the enzyme’s active sites
If temperature gets too high the reaction stops
This is because it causes the molecules to vibrate too much which can break some of the bonds holding the enzyme in shape
Enzyme’s active site changes shape - denatured (enzyme and substrate no longer fit together)
How does pH affect the rate of an enzyme-controlled reaction?
All enzymes have optimum pH
Above and below the optimum the H+ (acid) and the OH- (alkali) ions can disrupt the ionic and hydrogen bonds holding the enzymes tertiary structure in place.
Enzyme = denatured (active site changes shape)
How does substrate concentration affect the rate of an enzyme-controlled reaction?
The higher the substrate concentration the faster the reaction
Collisions between substrates and enzymes are more likely
Only up to ‘saturation point’ - all active sites are in use so increasing substrate concentration further will have no effect
How do competitive and non-competitive inhibitors affect the active site?
Competitive inhibitors - similar shape to substrate molecules, compete with substrate molecules to bind to active site and block the active site so no substrates can fit in.
Non-competitive - they bind to the enzyme away from its active site, which causes the active site to change shape so substrate molecules can no longer bind to it.
What is enzyme inhibition?
Enzyme activity can be prevented by enzyme inhibition - they bind to the enzyme that they inhibit (can be competitive or non-competitive)
